A way to observe url in urlbar of firefox, and get an event every time it changes

I need it for my firefox extension. I don't care about waiting the page load completely, I want only observe URL and get an event every time it changes, also when I do history back and forward.

edit: I saw An observer for URL change开发者_运维百科s (Firefox Extension), but i wondering if there is something much simpler, like an event that fires every time the url is part of an action, like page request, history back and forward ecc..

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https://developer.mozilla.org/en/Code_snippets/Progress_Listeners#Example.3a_Notification_when_the_value_in_Address_Bar_changes

Also How can i check if url of current browser tab is changed?

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SWFAddress has a Javascript library that lets you do just that.